This invention relates to a direct-acting servo valve suitable for use with a hydraulic drive system, such as a vibration tester, rolling mill, etc.
In this type of servo valve, a spool mounted in a body for axial movement of directly driven by a force motor comprising a yoke, a permanent magnet and a bobbin. This type of servo motor is characterized in that it is highly responsive as compared with other types of servo motors by virtue of the fact that its movable section can be made light in weight. This characteristic makes it suitable for use with a hydraulic drive system, such as a vibrating table, a rolling mill, etc.
In this type of servo valve, a spring is used as mechanical means for positioning the spool, and a sensor in the form of a differential transformer is used as electrical means to attain the same as disclosed in Japanese Patent Laid-Open No. 10198/80. However, some disadvantages are associated with the prior art. When a spring is used, the valve becomes poor in response (about 600 Hz), and difficulties are experienced in achieving high response (over about 1 KHz) even if a sensor is used.